This invention relates generally to infrared suppression devices and more generally to methods and apparatus for reducing infrared emission from gas turbines such as those used, for example, in helicopters.
In some helicopters used in hostile environments, gear boxes used to drive helicopter rotors are driven by gas turbine engines. Known gas turbine engines rotate at typically higher revolutions per minute (RPM) than the helicopter rotors. Known engines also include a tailpipe which channels exhaust overboard from the gas turbine engines. As a result of hot exhaust gases flowing therethrough, the operating temperature of a known tailpipe increases during engine operation, and thus, an infrared signal generated by the tailpipe also increases.
With recent advancements in weapons detection technology, there is growing recognition of the importance of reducing the infrared signature associated with gas turbine engines powering military aircraft and land combat vehicles. Moreover, infrared signature reductions facilitate reducing the possibility of detection and pursuit by enemy anti-aircraft forces including heat-seeking missiles. As a result, at least some known aircraft use a combination of infrared defensive systems. For example such systems may include a propulsion system infrared suppression, a suppression system to facilitate suppressing other infrared sources on the aircraft, infrared countermeasures, i.e., a jamming device, and/or improved aircraft paint. These defensive systems contribute individually and as a system to synergistically facilitate reducing the susceptibility of the vehicle to a missile attack, and as a result, such systems facilitate reducing aircraft vulnerability, while increasing aircraft, crew, passenger and payload survivability.
Generally, the largest source of infrared energy is emitted from the aircraft engine exhaust. More specifically, exposed metal surfaces within the exhaust pipe emit infrared electromagnetic radiation at all wavelengths after being exposed to the high temperature exhaust gases. Specifically, at least some known metal surfaces exposed to hot gases can emit large amounts of infrared radiation between approximately 1.5 and approximately 5.0 microns. Moreover, hot exhaust gases from the engine exhaust can include CO2, NO2, and/or H2O molecules that can emit infrared energy at wavelengths of approximately 1.4, 1.8-2.0, 2.6-2.8 and 4.24.3 microns, respectively, thus contributing to the infrared signature.
To facilitate reducing an aircrafts's susceptibility to an infrared missile attack, at least some known engines channel ambient air past at least some of the exposed visible surfaces to facilitate diluting exhaust gases discharged from the engine. However, at least one known infrared suppression system actually absorbs heat that is emitted from the gas turbine exhaust thus increasing a temperature of the infrared suppression system itself.